The aim of this proposal is to investigate the neural and endocrinological control of sex behavior in the South African clawed frog, Xenopus laevis. This experimental system offers direct endocrine control of stereotyped male and female sex behaviors linked to hormone-specific brain target regions. Two male sex behaviors, clasping and mate calling, and two female behaviors, receptive immobility and sustained knee flexion, will be characterized and hormones effective in restoring sex behaviors to castrates determined. Blood levels of testosterone, dihydrotestosterone and estradiol will be measured by radioimmunoassay in sexually inactive, sexually active, castrated and intact-gonadotropin injected frogs. Increasingly dilute amounts of behaviorally effective hormones will be administered until the minimum effective dose necessary to activate sex behavior is determined. The performance of castrated male and female frogs in a given behavior under identical hormone conditions will be compared. Any difference in the ability of one sex to perform heterotypical and homotypical behaviors will be reinvestigated using sex reversed frogs. A stereotaxic atlas of the Xenopus brain will be constructed. Autoradiographic studies of sex hormone concentration in frog brain reveal localization of male and female steroids to different brain areas. The neuroanatomical connections of these regions will be investigated with argyrophilic degeneration and axoplasmic transport techniques. The hormonal specificity of brain target regions which concentrate both testosterone and estradiol will be investigated autoradiographically with non-aromatizable androgens. Neural substrates for sex behaviors will be studied by placing small lesions in hormone uptake brain areas or regions connected to them and observing effects on male and female sex behaviors.